# Nonoverlapping clock generator

Discussion in 'The Projects Forum' started by andrea86, Sep 30, 2010.

1. ### andrea86 Thread Starter New Member

Sep 30, 2010
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0
Can anyone help me with nonoverlapping clock generator?
Why are these clock nonoverlapped?
I need an expalination.

2. ### Papabravo Expert

Feb 24, 2006
11,683
2,455
With non-overlapped clocks you can use all of the edges without violating set-up and hold-time restrictions. If the clocks overlap then the leading edge of the next clock precedes the trailing edge of the previous clock.

3. ### andrea86 Thread Starter New Member

Sep 30, 2010
12
0
I need an explanation why are clocks non overlapping?

Last edited: Dec 16, 2010
4. ### beenthere Retired Moderator

Apr 20, 2004
15,815
293
Perhaps you can post up the circuit?

5. ### Wendy Moderator

Mar 24, 2008
21,352
2,919
Older CPUs used to use them a lot, it was to keep data moving inside the CPU. Basically you make an oscillator, then add a simple phase shifter/Schmitt Trigger. Walla! Two separate clock signals that don't overlap. If you try to make two different oscillators this is almost impossible.

6. ### beenthere Retired Moderator

Apr 20, 2004
15,815
293
I question the 200 msec delay as stated. What is the master clock frequency and what devices are you using (by type number)?

7. ### andrea86 Thread Starter New Member

Sep 30, 2010
12
0
I need a good explanation.

Last edited: Dec 16, 2010

Apr 20, 2004
15,815
293
9. ### andrea86 Thread Starter New Member

Sep 30, 2010
12
0
Thank you,bat that's not a question.I only need an explanation
how does this circuits works,or why this circuit makes non-overlapping clocks?

10. ### Wendy Moderator

Mar 24, 2008
21,352
2,919
The answer is simple, phase shift. You have two identical frequencies (truly identical) which are shifted by some angular amount (which is why the RC circuit is there on the earlier replies).

You are making this complex, more so than it needs to be.

The circuits you are showing are depending on propagation delay of the chips. Over complicated, and there won't be much difference between edges, just enough.

11. ### Kit_Leong New Member

Dec 4, 2010
5
0
to andrea86,

Hello,Im using the same circuit u mentioned above for a 2 phase non overlapping clock signal http://tams-www.informatik.uni-hambu...-clock-gen.htm ,Im using it as a clock signal for my modulator/demodulator as I am doing a chopper stabilized bandgap reference circuit.Did you manage to get a non overlapping signal?I cant seem to be able to get it,I'm using mentor graphics for my simulation,attached is a picture of my waveforms and circuit,do you know why it is not overlapping?i already followed this schematic but still not getting the expected results

if u cant see the picture i attached,try looking here <snip>

Last edited by a moderator: Dec 4, 2010
12. ### Kit_Leong New Member

Dec 4, 2010
5
0

The pictures I tried to attach in the previous message are here,thanks.

13. ### eblc1388 AAC Fanatic!

Nov 28, 2008
1,543
104
It depends on understanding what limitations your simulation software has.

Here is a simulation done the free LTSpice IV.

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14. ### Kit_Leong New Member

Dec 4, 2010
5
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yea thats the same circuit you are using that i'm using as well,thats odd if a circuit can work on one software and not on another,currently I thought of something else but it seems too simplistic to work,though I did manage to get the expected results,what do you think of it?

I tried to put a Vpulse signal to 1 output,and for the 2nd output,I added a slight delay to the Vpulse so its shifted just nicely to look like a non overlapping waveform.

Is it ok to do this instead?but if it were that simple I dont think people will use more complicated circuits to get the job done now would they?Thanks.

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15. ### eblc1388 AAC Fanatic!

Nov 28, 2008
1,543
104
Anything that works for you works.

Kit_Leong likes this.